Because of the nature of a tape, especially a stiff fiber tape, existing tape heads maintain a tape trajectory from the tape supply reel to the point of application onto a tool that does not allow the tape to move significantly out of a single plane. Existing tape head designs are comprised of (1) a tape supply reel; (2) a tape driving and cutting device; (3) a compaction roller or shoe that impresses the tape on to the surface of the part in process; and (4) a tape backer take-up reel. In these prior implementations, these four items are mounted to a common rigid structure such that their relative positions are fixed.
A number of designs have provided limited independent freedom of motion of the compaction roller with respect to the other three elements described above. Some of the prior art designs have passive compliance built into the compaction roller or to the compaction roller rotational shaft support, while others have a controlled position displacement by means of a motor or linear actuator. The designs with compliance of the compaction roller provide this feature to allow tension control across the tape width and allow limited steering of the tape or to impart a correcting force to keep the tape tracking down the centerline of the compaction roller.
One example provides for a tape head where the compaction roller can articulate about an axis normal to the compaction roller tangent surface at the intended work surface contact point. This example also provides for an accumulation of fiber tape such that the compaction roller can perform rapid motions to accommodate surface normal vector changes without having to respond with the entire tape head structure immediately. However, the compaction roller work surface contact point is fixed in the plane of the supply reel so that lateral displacements of compaction roller require the entire structure to be displaced. Further, the necessary apparatus and control system requires numerous controls and actuators. The tape accumulation mechanism induces sharp bends in the tape and given the large dimensions of the entire assembly would not be advantageous for a multiple tape head system where close location of adjacent tape heads may be necessary.
During tape lay-down a tape head assembly is steered and oriented to keep the compaction roller's axis normal to the direction of travel and, normal to the work surface as the compaction roller lays tape along the tape center line. These motions require the entire mass and the entire volume of this structure to be accelerated, moved and decelerated imposing large demands for motor power and volume clearance around the tape head structure. The inertia is both translational and rotational for the tape head mass plus the rotational inertia of the supply reel. The supporting structure must also be larger and more massive to accurately place the tape head relative to the tool or mandrel surface. The fact that the tape reel must be moved generally with the compaction roller limits the size of this reel and accordingly the amount of tape that can be laid down on a part between tape re-loads.
Another example discloses a method to lay down fiber tape that utilizes multiple tape heads each laying down a single fiber tape in coordination with the other tape heads and a rotating mandrel tool to fabricate a single large fuselage section. This multiple head fiber tape machine provides for a considerable reduction in the time required to fabricate a large fuselage section. However, since it utilizes a prior art tape head design, the size of the fiber tape supply reel and its replenishment must be offset by the demands for space, as each tape head must be articulated during the lay-up process and be accessible for replenishment. The result is a very large heavy support structure required to maintain the tight positional tolerances between heads and limited tape head packing density during operation, limiting the number of heads that can be engaged in the lay-up process simultaneously.
A still further example exhibits a method and apparatus to provide a tape head that does not have to be rotated at the termination of each tape pass. This is accomplished by having two or more tape reels where, in one example, the two reels are at opposite sides of the compaction roller. While eliminating the need to perform the large rotations between the termination of one pass and the start of another, this design increases the overall weight and space required and the rotational moment of inertia. A support structure and motion control means would have to be larger and more powerful to accommodate this type of design.